This project concerns the elucidation ofthe structure and mechanism of protein prenyltransferases, and the application of insights gained from their structures in the development of new therapeutics for the treatment of cancer, and various parasitic and fungal infections. The two prenyltransferases, farnesyltransferase (FTase) and geranylgeranyltransferase type-1 (GGTase), catalyze an essential covalent modification of over 120 proteins by isoprenoid lipids (prenylation) that is required for localization to membranes. Most ofthe modified proteins are involved in cell growth and proliferation and include members ofthe Ras GTPase superfamily. Inhibition of prenyltransferases has proven to be an important target for development of therapeutics for diseases ranging from cancer to parasitic and fungal infections. Previously we have determined the structures of human FTase and mammalian GGTase, structurally defined the reaction intermediates, and examined the structures of their complexes with a variety of anti-cancer therapeutic leads. FTase and GGTase inhibitors (FTls and GGTIs) show promise for treatment of parasitics infections including malaria, Chagas disease, African sleeping sickness, Leishmania and fungal infections such as Candida albicans, which can be life-threatening in immuno-compromised patients with AIDS. This study aims to further our structural understanding of the fundamental mechanism of action and substrate or inhibitor specificities for human and pathogen enzymes. We anticipate that this will provide critical information for the development of inhibitors that selectively inhibit prenylation of specific target sequences to be used as new cancer therapeutics, and species-specific antifungals or antiparasitics. Our approaches use X-ray ' crystallography, site-directed mutagenesis, kinetics, and inhibitor synthesis. There are three main themes in the research: 1) Analysis of mechanism and substrate specificities ofthe mammalian protein prenyltransferases. 2) Structure-function analysis of protein prenyltransferases from human pathogens, including Candida albicans, Trypanosoma brucei, Trypanosoma cruzi and Plasmodium. 3) Understanding specificity and inhibition mechanisms of clinically important inhibitor complexes